Method for making stators for dynamoelectric machines

ABSTRACT

A method which involves aligning a stack of a plurality of loose laminations so that clamp bolt holes therein are held in an accurately aligned condition while the stack is compressed (in the vicinity of the bolt holes) between pads that simulate mounting pads in a compressor, and a means for applying a force localized in the bolt hole regions. The compressive forces are preselected to simulate and closely approximate the compressive forces that ultimately will be applied to the bolt hole regions under the heads of mounting bolts in a compressor. Since the stack is initially aligned before the compressive forces are applied and while the laminations are free to shift relative to one another, the various eccentricities and dimensional variations between the bore and bolt holes are transferred to the bore. Then, while the stack is held with the preselected compressive forces, the bore is shaped to be concentric relative to the bolt holes. One means that may be used to shape the bore is a tool known in the motor manufacturing art as a roller burnishing tool.

BACKGROUND OF THE INVENTION

The present invention relates to parts used in electric motors and, moreparticularly, to apparatus and methods for making stator assembliescomprising a laminated magnetic core and windings that are primarilyadapted for being bolted to mounting means within a hermetically sealedrefrigeration compressor.

Substantial work has been done heretofore in order to prevent loss ofbolt torque retention and to maintain a concentric air gap. For example,Hull U.S. Pat. No. 3,299,304 and Sisk U.S. Pat. No. 3,465,188 are bothdirected at solving this problem. While these patents primarily describewhat are known as "bonded cores", unbonded cores are also described inthe art by, e.g., British Pat. No. 1,192,791 which was published May 20,1970. Moreover, specific methods aimed at maintaining straight andconcentric bores are described in Reynolds U.S. Pat. No. 3,845,547, andGerstle U.S. Pat. No. 3,834,013. In the interest of brevity, the entiredisclosures of all of the patents just mentioned are now expresslyincorporated herein by reference for background purposes.

Another patent which describes equipment and methods pertaining toaxially compressed but unbonded cores in McMahon U.S. Pat. No.3,605,257. Generally, the approaches suggested by the above-mentionedpatents are less than fully satisfactory when unbonded cores are to beproduced, and problems still remain in producing unbonded hermetic coresthat will exhibit both good final mounting bolt torque retention andgood concentricity after having windings placed thereon and then beingbolted to compressor mounting means.

Accordingly, an object of the present invention is to provide new andimproved methods and apparatus that can be utilized to produce unbondedstator cores and/or stator assemblies that will exhibit good boreconcentricity and good bolt torque (or tension) retentioncharacteristics.

SUMMARY OF THE INVENTION

In carrying out the above and other objects of the invention, in oneform thereof, I provide a new and improved method which involvesaligning a stack of a plurality of loose laminations so that clamp boltholes therein are held in an accurately aligned condition while thestack is compressed, in the vicinity of the bolt holes, between padsthat simulate mounting pads in a compressor and a means for applying aforce localized in the bolt hole regions. The compressive forces appliedto the bolt hole regions are preselected to simulate and closelyapproximate the compressive forces that ultimately will be applied tothe bolt hole regions under the heads of mounting bolts when the core isbolted down in a compressor. Since the stack is initially aligned beforethe compressive forces are applied and while the laminations are free toshift relative to one another, the various eccentricities anddimensional variations between the bore and bolt holes are transferredto the bore. Then, while the stack is held with the preselectedcompressive forces, the bore is shaped to be concentric relative to thebolt holes. One means that may be used to shape the bore is a tool knownin the motor manufacturing art as a roller burnishing tool.

Collateral steps that are carried out in putting the invention intopractice may include: (1) punching laminations from sheet or stripmaterial, and preferably punching mounting bolt holes and wireaccommodating slots at the same station so that the dimensionalrelationships between such slots and holes will be held to thetolerances built into the dies used at such station; (2) annealing thelaminations to relieve stresses therein caused by the punching process,and preferably keeping the laminations in fixed orientation relative toone another; (3) breaking interlaminar bonds between adjacentlaminations in the event that they have been annealed in a stackedcondition and adjacent nitride or oxide layers have adhered to oneanother; (4) metering a number of laminations to form a stack of adesired height by means of weighing or by using a stack height selectingtool; (5) inverting the top lamination relative to the stack so that thepunching burrs thereon are directed inwardly along the stack; (6)insulating the winding slots in the stack of loose laminations with anysuitable apparatus as known in the art; (7) placing winding coils in thecore slots; (8) the core and windings are washed and baked; and (9)performing suitable tests such as surge, hi-potential, etc. on the woundcore, after which it is ready for assembly into a compressor housing.

It seems to be most convenient to compress the core and establish boreto bolt hole concentricity as described hereinabove after the wound corehas been washed and baked; but the compressing and bore working stepsmay be performed before the windings are inserted and after the stackhas been established.

When the preferred process as described hereinabove is practiced, it nolonger is a necessity to weld or adhesively bond the core (although suchmay also be done if desired), and thus savings may be realized in labor,material, welding atmosphere gas, and energy that would have to be usedfor welding or for curing adhesive material.

In accordance with another aspect of my invention, I provide apparatuswhich may be used in conjunction with practicing the method describedhereinabove. In one form, such apparatus may comprise a block havingpins that mate with the bolt holes in the core, and the block simulatesa compressor casting. The block is mounted in a four post die set, andthe apparatus further includes a mating block which preferably includeshardened pads that will slide over the pins and simulate the contactarea of bolts as the mating block is pressed against a core that hasbeen previously placed over the bolt simulating pins. Means are alsoincluded for applying a compressive force to one of the blocks whileother means constrain the other block from moving. The compressive forceis transmitted to the core by the hardened pads, and the force exertedby each pad is about the same as or slightly greater than the force thatwill be applied by bolt heads in a compressor. The apparatus furtherincludes a roller burnisher that establishes a concentric bore that isalso perpendicular to the block and mating block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of parts of an apparatusembodying the invention in one form that may be used to practice theinvention, and illustrates in some detail a lower block, a four post dieset, and a stator lifting ring;

FIG. 2 is a side elevation, with parts in section, parts in phantom, andparts removed, of apparatus that may be used to practice the invention

FIG. 3 is an inverted perspective view of a mating or top block anchoredto a top or sliding die shoe, these parts also being shown in phantom inFIG. 2; and

FIG. 4 is a side elevation of another form of apparatus that may be usedto practice the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With initial reference to FIG. 2, apparatus 11 is illustrated having astator 12 positioned therein, the stator including a laminated core 13having a number of wire accommodating slots 14 therein, and windings 16accommodated thereby.

The apparatus 11 includes a precision four post die set that includes alower die shoe 17, four die posts 18 anchored in the shoe 17, and a topor sliding die shoe 19 (more details of which are revealed in FIG. 3,and discussed hereinbelow). Anchored to the lower shoe 17, by anysuitable means such as bolts 21, is a lower block 22 which has anchoredtherein bullet nose pins 23 which simulate the number, size, and shapeof bolts that will be used in mounting the stator 12 in a compressorhousing. Good results have been obtained, for example, when the pins 23are precision made to be about 0.001 inch (0.0254 mm) less in diameterthan the diameter of the bolt holes 24 in the core 13.

When a stator lifting ring is to be used in conjunction with practicingmy process, the stator lifting ring 26 (see FIGS. 1 and 2) is positionedover the lower block 22, with the holes 27 in ring 26 accommodating thepins 23. The upper and lower faces 28, 29 of the lifting ring 26 areground so as to be flat and parallel to one another, and the lower block22 is also ground to have flat and parallel faces; so that when thelower face 29 of the ring 26 seats on the upper face 31 of block 22, theupper face 28 of ring 26 will be parallel (within machining accuraciesand tolerances) to a plane perpendicular to the die posts 18 and to thebore 32 of stator 12 after it is positioned thereover.

The lifting ring 26 includes four regions 33 that simulate the mountingpads of a compressor; and similar compressor mounting pad simulationregions 34 are provided on the block 22 so that the core 13 will rest onsimulated mounting pad regions whether the process followed includes oromits utilization of the lifting ring 26.

After the lifting ring 26 has been placed over the pins 23 (or after adecision has been made to not use the ring 26); the core 13 is placed onthe pins 23 and the lower face bears upon the compressor mounting padsimulating regions 33 or 34, as the case may be.

It should here be noted that the core 13 may or may not at this timehave windings 16 thereon and, further, if not wound; may or may not haveground insulation in the slots therof (although it is preferred that thecore at least be insulated, with the insulators helping to hold the corelaminations together in a stack).

It is important however, that the individual laminations 36 besufficiently loose relative to one another to be able to shift laterallywithin the stack. Then, when the close tolerance pins 23 enter the boltholes 24 of individual laminations, the laminations will be free toshift relative to one another (if necessary) so that the entire stack oflaminations will be laterally positioned on the pins 23. However, aswill be understood by persons skilled in the art, other parts of thevarious laminations may not be aligned with one another. For example, asdescribed in Bair U.S. Pat. No. 3,762,198 (dated Oct. 2, 1973); aslamination stock is advanced through punch presses, stretching orelongation of the stock may occur. Since the bolt holes 24 and finalbores 32 of laminations 36 are usually punched at different stations,any such elongation occurring between the stations will result in someeccentricity between the bore and the bolt hole circle. Furthermore,since different dies are used at different punch press stations;respective die manufacturing tolerances may be cumulative in effect, andfurther contribute to eccentricities between the bore and bolt holes (orbolt hole circle).

The actual outer peripheral shape of the laminations 36 is not importantfor the purposes of the present discussion (or the present invention),but the laminations 36 may be: round and configured substantially asshown in Hull U.S. Pat. No. 3,299,304 (issued Jan. 17, 1967); orgenerally rectangular or square and configured as shown, for example, inGerstle U.S. Pat. No. 3,834,013 (issued Sept. 10, 1974).

It is emphasized that, regardless of the shape of the laminations 36,eccentricities between the bore and bolt hole circle in the finallamination may and usually do occur, and it is not of real importance asto what causes the problem. For example, it is not of great importancewhether the cause for the eccentricities is due to strip materialstretching, forces exerted on lamination teeth by windings, staggeredlaminations, or due to other reasons as variously proposed in thehereinabove referenced Reynolds, Gerstle, Bair, Hull, or Bair U.S. Pat.No. 3,762,041 (the entire disclosures of all which are incorporatedherein by reference).

Although the problem of nonconcentric bores has been identified, andvarious solutions have been hopefully suggested, it has now been foundthat good results can be consistently attained by accurately aligningthe bolt holes (and thus the bolt hole circles) and relatively shiftingthe laminations as may occur when the bolt holes are aligned so as tocause eccentricities between the bolt circles and bore to occur at thebore; simulating the mounting conditions and stresses that the core willexperience in a compressor housing; and then-while the core is sostressed-removing the bore eccentricities while preventing thelaminations from shifting relative to one another. In other words, afterthe laminations are mutually located in aligned fashion at the boltholes and dimensional variations are concentrated at the bore, and whilethe core is prestressed, the bore is made concentric with the bolt holecircle. This approach is markedly different from: previous ones thathave been directed to shaping or straightening a bore while thelaminations could shift at the bolt holes or while the core was notprestressed and located in a precise manner; previous ones that soughtto make the core as solid and rigid as possible, and may or may not haveincluded a bore shaping step; and previous ones that concentrated oncorrecting tooth tip irregularities at the bore.

With all of the above in mind, reference is now again made to FIGS. 1, 2and 3 of the drawings. After the stator 12 is positioned in parallelismon the mounting pad simulating regions 33 (or 34), the sliding die 19 ofFIG. 3 is positioned thereover on die posts 18, with bushings 37surrounding the posts 18. When in this position, the mating block 38(which is fastened to die 19) overlies the stator, and the pins 23 arepositioned to enter hardened pads 39 which are carried on block 38 andwhich simulate bolt heads that contact the core face when it is boltedinto a compressor housing. Then, as die 19 moves toward die 17, pins 23enter not shown hardened bushings that are carried in block 38.

These bushings are provided to reduce wear of parts, and thus ensurethat close dimensional tolerances will be maintained even after manycycles of apparatus operation.

Thereafter, any suitable press (e.g., one using a hydraulic ram) forcesthe upper die and lower die toward one another so that the core 13 iscompressed in the bolt region by a force closely approximating thecompressive force that will be applied by bolt heads when the core ismounted in a compressor housing.

For example, when a one quarter inch (6.35 mm) hex-head bolt or a number8 hex-head bolt is to be used, for mounting (without a washer under thehead); and the bolt is to be torqued down with a force of forty-five tofifty-five inch-pounds; the bolt head will exert an axial force of about1500 pounds (682 kg) at each bolt hole. I have found that forcing thedies together with five tons of force results in a force of about 1500pounds being exerted by pads 39 on the core.

Thereafter, I pass a roller burnisher through opening 41 in the upperdie shoe 19, and burnish out the various eccentricities in the statorbore 32; then separate the die shoes; and then lift the stator 12 fromthe lower die with lifting ring 26.

In FIG. 4, I have shown a modified form of apparatus which is alsouseable for practicing the present invention. For the sake of simplicityand clarity, the same reference numerals are used for components in FIG.4 that are either identical to, or the same in function, as componentparts described in full in conjunction with FIGS. 1-3. Thus, those partswill not be further described in conjunction with FIG. 4 except to callattention to their presence. Thus, the apparatus of FIG. 4 includes,mounted on a machine frame 42, four die posts 18, an upper die shoe 19and lower die 17; upper and lower blocks 38, 22; four pins 23 carried byblock 22, hardened pads 39 suspended from block 38; and a lifting ring26.

As will be appreciated from a review of FIG. 4, a hydraulic ram 43(although a pneumatic or other type of prime mover could be used) issupported at the top of the frame 42 and the rod 44 thereof isinterconnected with the upper block 38 by means of a bolt 46. On itsupward stroke, the ram 43 raises the block 38 and thus the die shoe 19.On the other hand, as the ram 43 extends, it bears against a countersunksurface 47 of the upper die and moves the die 19 along with block 38into compressive engagement with the face of the stator 12.

A hydraulic motor 48 is also supported on the frame 42 and this motorsupplies power through belt 49 to a Hydramat drill unit 51 to which airpower is also supplied through a not shown conduit. When air is suppliedto the drill unit 51 (after upper die shoe 19 has closed on the stator12), the drill unit automatically extends the shaft 52 upwardly so thata roller burnisher attached to the upper end of shaft 52 rises into thebore 32. During this time, the burnisher 53 is rotated by the shaft 52and eccentricities in the bore 32 are burnished out in the same manneras described hereinabove.

The drill unit 51 then lowers the burnisher 53, ram 43 raises die shoe19; and two stripper cylinders 54 are actuated which thereupon extendrods 56, and raise lifting ring 26 so as to elevate the stator 12 andstrip it from the pins 23.

As noted hereinabove, the roller burnisher may be of any of those typescommonly used in the industry and may be, for example, one obtained fromthe source identified in Reynolds U.S. Pat. No. 3,845,547--i.e., theGustaf Wiedeke Company of Dayton, Ohio.

Apparatus such as that shown in FIG. 4 has now been used successfully toproduce stator cores having desired bore diameter limits of from 2.3985inches to 2.4015 inches (60.923 to 60.998 mm), having a core or stackheight of up to one and three quarter inches (44.4 mm), and horsepowerratings of from one-eighth to one-third (93.25 to 248.7 watts) output.Those cores have then been positioned on compressor mounting pads,centered with an expandable fixture or mandrel of the type shown, forexample, in Geisenhaver U.S. Pat. No. 3,464,107 (issued Sept. 2, 1969);and bolted down essentially as described in the Geisenhaver patent.Experience has now shown that rigid control of the parallelism of thedie shoes 17, 19, and blocks 22, 38 with a rugged frame as shown at 42(in FIG. 4), and rigid mounting of drill unit 51 on the frame 42 is alsoimportant. It is for this reason that frame 42 is part of a HannifinHydraulic Press. The rigid mountings just discussed result in properlyfinished cores which can be assembled into compressors with virtually noair gap rejects. In this connection, it should be emphasized that "airgap" failures or rejects at the point of compressor assembly can hardlybe tolerated, and reject rates of more than about 1% would be completelyunacceptable and essentially preclude the use of a process such as theone of the present invention in a competitive high volume productionmotor industry.

Trials involving cores made by the process taught herein have now alsoshown that successful practice of the invention with a roller burnisherseems to require attention to and close control of other manufacturingsteps that are followed when manufacturing stator laminations and cores.

For example, early trials that were made resulted in non-uniform resultsuntil finally it was determined that initial punching dimensionaltolerances and annealing practices could prevent successful practice ofthe invention.

More specifically, with cores sized as described hereinabove, thebearingizer would flare the bore of the core when the total indicatedrunout (TIR) of the individual laminations exceeded 0.011 of an inch asmeasured from the center of the winding slots (or bolt hole centers) tothe bore. On the other hand, more consistent results were obtained aftera lamination die was carefully repaired and reworked so that dimensionaltolerances of plus or minus 0.0002 of an inch of the nominal designdimensions were held and the TIR between winding slots and bores (inlaminations made with the reworked die) was only 0.003 of an inch. Coresmade from these more accurately dimensioned laminations could then bemore consistently bearingized without distorting or flaring the bore ofthe core. Thus, while cores made of laminations having 0.011 of an inchTIR were not generally suitable for practicing the invention; cores madeof laminations having 0.003 of an inch TIR were-and the amount of TIRthat would be tolerable for bearingizing (also called roller burnishing)would appear to be between about 0.003 and about 0.011 of an inch (about0.0762 mm to 0.2794 mm).

Still further trials revealed that annealing practices could introducebore distortions and resulting bore eccentricities that could not beproperly and reliably remedied by practicing the invention. For example,trials showed that laminations produced to have 0.003 of an inch TIRcould still be made into cores having air gap failures if thelaminations had been carried through an annealing oven while beingsupported from the bore on horizontally disposed supports or bars. Itnow appears that the weight of the lamination material can stretch orelongate the bore when the lamination is so supported at elevatedannealing temperatures.

Further trials confirmed that laminations produced to 0.003 of an inchTIR and also annealed while laying flat (so that the bore was notstressed during anneal) could be produced into good stators bypracticing the present invention. In other words, when these otherprocesses are controlled or modified to be as just described, it appearsthat not more than about one out of one hundred stators produced bypracticing the invention will have air gap problems when being assembledinto a compressor. The trials referred to above have also shown that thealigning pins may be of 0.187 or 0.188 of an inch in diameter (plus orminus 0.0002 of an inch) for bolt holes of 0.190 of an inch diameter(plus or minus 0.0002 of an inch) and still yield good results when theannealing procedures and slot to bore TIR are controlled in the mannerdiscussed hereinabove.

In addition to the savings in material and energy, as discussedhereinabove, motors manufactured according to the teachings of thepresent invention exhibit good bolt torque retention, even aftercompressor dehydration processes. Thus, cores made as taught herein,exhibit desirable torque retention characteristics of the type describedin the above-referenced Hull patent, and yet do not need to be "bonded".

While in accordance with the patent statutes, I have described what atpresent are considered to be the preferred embodiments of my invention,it will be obvious to those skilled in the art that numerous changes andmodifications may be made therein without departing from the inventionand it is therefore aimed in the appended claims to cover all suchequivalent variations as fall within the true spirit and scope of theinvention.

I claim:
 1. A method of manufacturing a bolt-down hermetic compressorstator comprising a core made up of a plurality of laminations having aconcentric central bore for accommodating a rotor, a number of conductoraccommodating slots having conductor material accommodated therein, anda plurality of mounting bolt receiving apertures and wherein thedimensional variations between the apertures and bore is notsubstantially greater than about three thousandths of an inch; themethod involving the use of apparatus located at a fixed location thatincludes a ram and a burnisher, the method comprising: accuratelyaligning the bolt receiving apertures of a stack of loose laminationsand compressing the loose stack in the vicinity of the apertures with apredetermined force applied by the ram of said apparatus and with theforce localized at the regions of the apertures so that dimensionalvariations between the apertures and bore are concentrated at the bore;shaping the bore with said burnisher of said apparatus while thelaminations continue to be aligned and compressed by said ram of saidapparatus, so that the bore is concentric relative to the location ofthe apertures; and releasing the compression on the stack oflaminations.
 2. The method of claim 1 wherein the dimensional tolerancesof the laminations are held, during manufacture, to a maximum of notmore than about three thousandths of an inch total indicated runout. 3.The method of claim 1 further including: annealing the laminations priorto aligning and compressing the stack; and supporting the laminationsduring the annealing cycle so that the laminations are not subjected tostresses that tend to deform the bore.
 4. The method of claim 1 whereinthe apertures are substantially round holes, and aligning the aperturescomprises placing pins in the apertures wherein the pins have a diameterthat is not more than about three thousandths of an inch smaller thanthe diameter of the apertures.
 5. The method of claim 1 wherein windingmaterial is placed in the slots of the core before the stack iscompressed and before the bore is shaped.
 6. A method of manufacturing abolt-down stator comprising a core made up of a plurality of looselaminations having a concentric bore for accommodating a rotor, a numberof conductor accommodating slots having conductor material accommodatedtherein, and a plurality of mounting bolt receiving apertures, whereindimensional variations between the apertures and bore are less thaneleven thousandths of an inch; the method involving the use of apparatuslocated at one predetermined location that includes a ram and aburnisher, the method comprising: accurately aligning the bolt holes ofthe plurality of loose laminations and relatively shifting thelaminations, thereby to cause eccentricities between the bolt holelocations and bore to occur at the bore; simulating, while using saidram of said apparatus, the mounting conditions and stresses that thecore will experience when ultimately mounted for use by compressing saidcore from a free state while using said ram of said apparatus; andremoving the bore-located eccentricities with said burnisher of saidapparatus while preventing the laminations from shifting relative to oneanother while the mounting conditions continue to be simulated by saidapparatus while using said ram at said predetermined location.
 7. Themethod of claim 6 wherein the bore and bolt holes are held inparallelism while the mounting conditions are being simulated.
 8. Themethod of claim 7 wherein the dimensional tolerances for each laminationduring manufacture thereof are held to a maximum of not more than aboutthree thousandths of an inch total indicated runout between the bore andbolt hole locations.
 9. The method of claim 8, further includingannealing the laminations prior to aligning the bolt holes, andsupporting laminations with the bore thereof oriented along a generallyvertical line so that the laminations are generally horizontal, wherebythe weight of the lamination material is prevented from tending todistort the bore during the annealing cycle.
 10. The method of claim 6wherein winding material is placed in the slots prior to aligning thebolt holes.